1,720,957 research outputs found
Investigation of Aging Effects on Combustion and Performance Characteristics of Mining Engines
No full textThe sustainability of mines is becoming ever more important to reduce the greenhouse gas footprint and keep the resources extraction economically sustainable. Despite the electrification and hybridization trend of mining equipment, Diesel engines are still expected to maintain their importance as a primary source of power especially for open pit equipment, thanks to their longer operating range. However, in order to keep high efficiency and minimize fuel consumption for the entire operating life it is crucial to understand and tackle the ageing effect on the engine performance. In this research a 500-h durability test was performed on a Liebherr mining engine, with the aim of better understanding how ageing affects the combustion process and engine performance (power and fuel consumption), and how this effect can be compensated. Experimental results show a 1% specific fuel consumption increase, ascribable to injector aging. Moreover, with the objective of emphasizing other possible opportunities to further reduce fuel consumption, the possibility of cancelling cylinder-to-cylinder disparities (maximum IMEP variations of 7% compared to the average value of 12 cylinders) and optimizing the calibration setting near the reliability limits (BSFC decrease by 0.7%, compared to the base calibration), were investigated in the paper. The role of cylinder pressure-based closed loop control systems as enabling technology to seize these potential benefits is discussed in the article
Application of a model for optimizing steady state and transient control of hydraulic dynamometers
No full textWater brakes are still used in engine test cells, due to their compactness, low inertia and high reliability. Compared to dynamic brakes (i.e., electric motor-generators), water brakes do not require bulky and expensive infrastructures (high-power connection to the grid, inverter cabinets, etc.), while in comparison with eddy current brakes they are less expensive and require lower maintenance. However, water brakes are often considered suited for steady-state tests, due to poor transient capability and steady state speed accuracy. The brake load torque is usually controlled by means of a control valve, that can be positioned both on the water inlet pipe (in-flow control) or on the outlet side (out-flow control): in fact, the braking torque is related to the impeller speed and the amount of water trapped inside the machine. Flow control valves, however, are prone to hysteresis and their dynamic performance is usually not satisfactory. Furthermore, they are expensive, so that they may represent a significant percentage of the total cost of the system. The paper shows how the brake can be modeled, allowing to assess the effect of braking torque regulating systems on transient performance. The approach allows testing in a simulation environment unusual braking torque control technique: at first, the model has been used to assess the torque regulation capabilities guaranteed by the use of a variable speed feeding pump. Results shows that transient performance greatly depends on the pump speed variation capabilities. The model proved to be an efficient tool to evaluate different control solutions, either based on inlet or outlet flow control, and it will be used in the future to design a new control system for water brakes
The actigraphic evaluation of daytime sleep in central disorders of hypersomnolence: comparison with polysomnography
No full textSTUDY OBJECTIVES: The role of actigraphy in central disorders of hypersomnolence (CDH) is expanding but evidence of reliability with polysomnography (PSG) is scarce and provided only during nighttime. We explored the agreement between actigraphy and continuous 24-hour PSG at CDH diagnosis. METHODS: Forty-four consecutive drug-naïve patients (28 narcolepsy and 16 idiopathic hypersomnia [IH]) underwent actigraphy during 24 hours of free-running PSG, during multiple sleep latency test (MSLT) and 13 of them also during maintenance of wakefulness test (MWT). Daytime and nighttime sleep features and MSLT and MWT mean sleep latencies (mSL) were estimated with the actigraphic algorithms by Cole-Kripke (CK), Sadeh (Sad), and University of California San Diego (UCSD). Agreement to corresponding PSG measures was assessed with Bland-Altman plots. RESULTS: Nighttime-total sleep time (TST) in narcolepsy was significantly underestimated with CK (bias 27.8 minutes, 95% CI 13.7 to 41.9) and Sad (bias 56.7 minutes, 95% CI 38.8/74.5). Daytime-TST was overestimated in IH and narcolepsy with all algorithms (CK: bias -42.2, 95% CI -67/-17.4; Sad: bias -30.2 minutes, 95% CI -52.7/-7.7; UCSD bias -86.9 minutes, 95% CI -118.2/-55.6). 24-hour-TST was overestimated by CK and UCSD in IH (CK: bias -58.5 minutes, 95% CI -105.5/-11.5; UCSD: bias -118.8 minutes, 95% CI -172.5/-65), and by UCSD in narcolepsy (bias -68.8 minutes, 95% CI -109.3/-38.2). In the entire cohort, actigraphy overestimated MSLT mSL but not MWT mSL. CONCLUSIONS: Conventional actigraphic algorithms overestimate 24-hour TST in IH and underestimate nighttime TST in narcolepsy. These discrepancies call for the cautious application of actigraphy in the diagnostic process of CDH and the development of new quantitative signal analysis approaches
Application of Low-Cost Transducers for Indirect In-Cylinder Pressure Measurements
Full text linkThe aim of this work is to present the results achieved in the evaluation of combustion metrics using low-cost sensors for the indirect measurement of cylinder pressure. The developed transducers are piezoelectric rings placed under the spark plugs. Tests were carried out on three different engines running in various speed and load conditions. The article shows the characteristics of the signals generated by the piezo-ring sensors, compared to those coming from laboratory-grade pressure transducers: Focus is to assess the achievable accuracy in the determination of frequently used combustion metrics, such as those related to knock intensity (Maximum Amplitude of Pressure Oscillations, MAPO), combustion phasing (MFB10, MFB50, ...), and peak pressure. Despite some issues related to the variation in sensitivity (temperature effect) to mechanical noise at high engine speeds and to signal deviation from the actual cylinder pressure trace in some portions of the engine cycle, the article shows that combustion metrics evaluated using low-cost sensors are meant to be used for combustion feedback control
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Development of a Predictive Pressure Waves Model for High-Pressure Common Rail Injection Systems
Full text linkOver the last years, automotive industries drove a great amount of research in the field of advanced combustion techniques minimizing carbon dioxide emissions. The so-called Low-Temperature Combustions (LTC), characterized by the self-ignition of highly premixed air-fuel mixtures, represent a promising solution to achieving high efficiency and ultralow emissions of nitrogen oxides (NOx) and particulate matter. Among these, gasoline Partially Premixed Combustion (PPC), obtained through the high-pressure direct injections of gasoline, showed a good potential for the simultaneous reduction of pollutants and emissions in compression ignited engines. However, when multiple injections per cycle are performed (with hydraulic-assisted needle opening), combustion stability might be compromised by the wave effects in the hydraulic system, which produce incoherence between the requested and injected fuel. This work presents a model-based pressure waves reconstruction strategy, based on a control-oriented model of the high-pressure common rail injection system fueled with gasoline. To determine the hydraulic system's behavior during the injection process, a specifically designed flushing bench with a high-frequency acquisition system has been developed. Experimental activities have been carried out to highlight fuel pressure fluctuations with single and double injection patterns. Through the analysis of the acquired data, the key parameters (characteristic of the system) have been identified and the accuracy of pressure waves reconstruction has been evaluated, always returning errors lower than 2% between measured and estimated instantaneous pressures. Different fuel types, injectors, and rail positions have been tested to highlight the robustness of the approach. Based on the instantaneous pressure trace estimated with the control-oriented model, a fuel quantity Fluctuation Correction Strategy (FQC), implementable on a standard engine Electronic Control Unit (ECU), has been developed. The obtained results confirm the potential to reduce fuel quantity oscillations in multiple-injections systems
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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